The present invention relates to a data relay apparatus for processing and restoring data to relay it from a communication device to another, more particularly to a voice data relay apparatus for compressing and decompressing voice data to relay it from a communication device to another.
An asynchronous transfer mode (hereinafter referred to as ATM) multiplexer which relays a voice call by use of an ATM network has been known as a relay apparatus for relaying voice data to a communication apparatus including a private branch exchange (hereinafter referred to as PBX) and the like. In such an ATM multiplexer, voice data to be relayed is compressed/decompressed so that a voice is compressed to be transmitted on the ATM network.
For example, a consideration is given to a case in which an ATM multiplexer c3301 and an ATM multiplexer d3302 perform relaying of a voice call between a PBX b3201 and a PBX e3202 in FIG. 3A.
As to a direction in which voice data tends from the PBX b3201 to the PBX e3202, the ATM multiplexer c3301 compresses the voice data received from the PBX b3201, and transmits the voice data to the ATM multiplexer d3302 via the ATM network 3101. The ATM multiplexer d3302 decompresses the voice data received, and then transmits the voice data to the PBX e3202. On the other hand, as to a direction in which the voice data tends from the PBX e3202 to the PBX b3201, the ATM multiplexer d3302 compresses the voice data received from the PBX e3202, and then transmits the voice data to the ATM multiplexer c3301 via the ATM network 3101. The ATM multiplexer c3301 decompresses the voice data received, and transmits the voice data to the PBX b3201.
A consideration is given to a case in which in FIG. 3A, to relay the voice call between a TEL a3401 and a TEL i3402 by use of a path passing through the PBX b3201, the PBX e3202 and a PBX h3203, the ATM multiplexer c3301 and the ATM multiplexer d3302 perform relaying of the voice call between the PBX b3201 and the PBX e3202, and the ATM multiplexer f3303 and the ATM multiplexer g3304 perform relaying of the voice call between the PBX e3202 and the PBX h3203.
Here, assuming that to relay the voice call between the PBX b3201 and the PBX e3202, the ATM multiplexer c3301 and the ATM multiplexer d3302 compress and decompress the voice data, and to relay the voice call between the PBX e3202 and the PBX h3203, an ATM multiplexer f3303 and an ATM multiplexer g3304 compress and decompress the voice data, the voice data of the voice call will be subjected twice to the compression and decompression as shown in FIG. 3B. Repetition of the compression/decompression of the voice data is not desirable because deterioration in a quality of the voice data is brought about.
For this reason, in the conventional system, a PBX recognizing that the PBX itself is not at an end of a relay path, that is, that the PBX itself only relay a voice call, has instructed an ATM multiplexer connected thereto not to execute the compression/decompression of the voice call. The ATM multiplexer that received the instruction has not executed the compression/decompression of the voice data of this voice call. Thus, the compression/decompression have not been executed repeatedly.
For example, in FIG. 3A, when the voice call between the TEL a3401 and the TEL i3402 is relayed by use of a path passing through the PBX b3201, the PBX e3202 and the PBX h3203, the PBX e3202 accommodating none of the TEL a3401 and the TEL i3402 recognizes that the PBX e3202 itself is not at the end of the path, that is, that the PBX e3202 itself only relays the voice call. Then, the PBX e3202 instructs the ATM multiplexer d3302 and the ATM multiplexer f3303 not to execute the compression/decompression of the voice data as to this voice call. Upon receipt of this instruction, the ATM multiplexer d3302 and the ATM multiplexer f3303 do not compress and decompress the voice data as to this voice call, and relay the voice data transmissively. Thus, the compression/decompression of the voice data as to this voice call is performed only once between the ATM multiplexer c3301 and the ATM multiplexer g3304, as shown in FIG. 3C.